15
51-638 Echotel Model 338 Two-Wire Ultrasonic Transmitter
Open Channel Flow Applications
Far end blocking is used in open channel flow applications
to force a zero flow value when the level is below the
chosen value. This allows the totalizer to stop recording
flow when the level drops below the preset value. If the
liquid level in the flume or weir falls below this value the
338 will:
1. Indicate "No Flow" on the LCD module
2. Hold last valid mA current value
NOTE: When the liquid level is above the far end blocking section the
calculation of level, volume, or open channel flow is based on
the programmed tank dimensions; therefore, the measured or
calculated process values are not influenced by the far end
blocking value.
NOTE: P07, P08, and P09 are not currently used with the Model 338
transmitter.
1.6.2 mA Current Output Settings
P10:
4 mA current output value
P11:
20 mA current output value
The mA current output values are calculated according to
the Measurement Mode that was selected in P01. For %
measurements (LEV or VOL) the 4 mA and 20 mA values
are entered in the relevant engineering units of LEV (ft, in,
m, or cm) or VOL (gal, ft3, m3, or liters).
Though P10 and P11 are usually set with 4 mA at the
bottom of the tank and 20 mA at the top, they can be
reversed with 20 mA at the bottom and 4 mA at the top.
P12: -a
Fail-safe Indication
Factory default value for P12 is: 0
The Model 338 continuously performs diagnostic checks
on the electronics and transducer, and confirms that the
unit has been configured properly. Refer to
Section 1.8,
Diagnostic Error Codes,
for a listing of all the errors codes
that can be displayed by the 338 transmitter. P12 is used
to set the desired mA output value if any faults are detect-
ed. The fail-safe mA values shown below are in accordance
with the NAMUR NE 43 standards.
c
Fault Values
0
Hold last value
1
3.6 mA
2
22 mA
